How to Test EHV Lightning Arrestor

TESTING of EXTRA HIGH VOLTGE LIGHTNING ARRESTOR

- For finding out faulty LA & decision making on replacement.

SUDHIR KUMAR SRIVASTAV

AGM-RAPDRP

NTPC LIMITED, NEW DELHI

Sudhirksri1@gmail.com

Abstract -This paper gives an insight of, how to test Extra High Voltage Lightning Arrestor, to come to a conclusion that whether we may continue with existing LA or there is a need to replace the LA with new one.

Keywords:      LA (Lightning Arrestor)

                        RLA (Residual life assessment)

                        AC (Alternating Current)

                        DC (Direct Current)

                        EHV (Extra High Voltage)

I. INTRODUCTION

A lightning arrester is a device used on electrical power systems to protect the insulation and conductors of the system from the damaging effects of lightning. When a lightning surge travels along the power line to the arrester, the current from the surge is diverted through the arrestor, in most cases to earth. Their purpose is to limit the rise in voltage when a power line is struck by lightning or is near to a lightning strike. If protection fails or is absent, lightning that strikes the electrical system introduces thousands of kilovolts that may damage the transmission lines, and can also cause severe damage to transformers and other electrical or electronic devices.

Lightning arresters built for EHV substation use are impressive devices, consisting of a porcelain tube several feet long and several inches in diameter, typically filled with disks of zinc oxide. A safety port on the side of the device vents the occasional internal explosion without shattering the porcelain cylinder. Lightning arresters are rated by the peak current they can withstand, the amount of energy they can absorb, and the breakover voltage that they require to begin conduction.

With the passage of time & with striking of multiple lightning, the conditions of LAs get deteriorated. But in Extra High Voltage (EHV) system, it is very difficult to come to a conclusion on replacement of old Lightning Arrestor.

In early days, only break down maintenance were in process, where electrical equipment were replaced with new one on its damage. Break down of equipments develops some disastrous situation, recovery of which is very time & resource consuming. Also there is every chance of damage of nearby equipments on break down of any equipment. So to avoid this situation, preventive maintenance have been started. With this practice we replace the equipments after a predefined time, without going into the detail of its healthiness.

In late years predictive maintenance / condition based monitoring / residual life assessment were started to optimize the cost & running time of any equipment.

In case of LA it is very difficult to do RLA & also there is no proven method to test it for taking any concrete decision on healthiness of equipment. Even leakage current meters of most of LAs are not giving correct picture of resistive current & healthiness of equipment.

With the experience & studies on the system we may say that, in addition to third harmonic resistive current measurement of LA, following more tests can be done to decide about the healthiness of LA:

1.    DC component of leakage current.

2.    Thermal scanning of LA

3.    Tan∂ measurement of different stakes of LA.

II. DIFFERENT TYPE OF TEST / MEASUREMENT ON LA

To measure DC component of Leakage curren

Take a new / healthy LA connected with charged EHV system.

• Connect a full wave AC to DC bridge coveters in parallel to leakage current meters, as shown in figure.
• Disconnect the leakage current meter from circuit so that full amount of leakage current flows through bridge circuit.
• Measure the DC component of leakage current (I1) from the bridge as shown in figure.

Do the same process for all the LAs. If DC component of leakage current of any LA is more than two times than that of new / healthy LA, we may short it for other testing.

Infrared Imaging of LA

Infrared Imaging of the LA shall be done after sun set to avoid any error in temperature measurement. If measured temperature through thermal scanning of any LA is 3°C more than the temperature of new / healthy LA, we may short it for other testing. This thermal scanning shall be done when LAs are connected to charged EHV system.

Tan∂ measurement of different stakes of LA

This test is done for disconnected LA from system. Tan∂ test of any equipment is done for resistive / leakage current measurement. These tests are normally done to check the healthiness of insulating material. Though LA is not an insulator but a non linear resistance element, we may treat it as insulator for test voltage and Tan∂ value of different stakes can be measured. If tan∂ value of any stake of LA is more than two times than that of new / healthy stake, we may short it out for other test.

III.  Conclusion

Any LA whose DC component of leakage current is more than two times than that of new / healthy one, measured temperature through Infrared Imaging of any LA is 3°C more than the temperature of new / healthy LA. And tan∂ value of any stake of LA is more than two times than that of new / healthy stake we may conclude that the LA is defective and there is an urgent need to replace the LA with new / healthy one.

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Inflated electricity Bill,....Why? ----- Part-II

REASON FOR FAST RUNNING OF ELECTRIC METERS  - Part-II

         - Why bills of electric consumption suddenly increased when          electromechanical meters replaced with electronic meters?

SUDHIR KUMAR SRIVASTAV

AGM-RAPDRP

NTPC LIMITED, NEW DELHI

Sudhirksri1@gmail.com

This is in continuation of my previous blog Inflated Electricity Bill…Why?’

There is one more reason for inflated electricity bill to single phase consumers as described below:.

In case of normal circuit as shown above:

• Current across the meter = I
• Voltage across the meter = V
• Power flow through meter W = V I CosØ 
• Energy recorded by meter P = W t

As V is actual voltage, I is actual current & CosØ is actual power factor, the energy recorded by meter shall be actual.

But in case the neutral of the meter is disconnected from the pole (supply side), and neutral side of the load is earthed as shown above, following will be the condition:

·         Phase will be available to load, through energy meter. Current will flow through the energy meter and power will be available at load, as second point of load is earthed.

·         In case of electromechanical meters, current through meter will be I. But voltage across meter shall be zero, resulting NIL record on energy consumption.

·         But in case of electronic meter, a feature is made available in the meter that, if current is flowing through current coil & there is no voltage across voltage coil, the calculation of power shall be based on normative value of single phase voltage i.e. 250 Volt & based on normative value of power factor i.e.  1.

·         In such a situation, if actual voltage of supply is 220 volt & actual power factor is 0.95, the actual energy flow shall be = 220 x I x 0.95 x t (Here 220 is voltage, I is current, 0.95 is PF & t is time)

·         But due to broken neutral, normative value of voltage & PF shall be 250 V & 1 and recorded energy through energy meter shall be = 250 x I x 1 x t. (Here 250 is normative voltage, I is actual current, 1 is normative power factor & t is time).

·         So % increase of recorded power w.r.t. actual consumed power shall be =

                         (250 x I x 1 x t  -   220 x I x 0.95 x t)*100/(220 x I x 0.95 x t)  = 19.6%

So we can conclude that, if actual voltage is 220 V, actual power factor is 0.95, but neutral circuit of meter is broken and load is connected between phase & earth, the energy recorded by electronic energy meter may be 19.6% more than actual energy consumption.

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Inflated Electricity Bill....Why?

REASON FOR FAST RUNNING OF ELECTRIC METERS

- Why bills of electric consumption suddenly increased when electromechanical meters replaced with electronic meters?

SUDHIR KUMAR SRIVASTAV

AGM-RAPDRP

NTPC LIMITED, NEW DELHI

Sudhirksri1@gmail.com

Abstract -This paper gives an insight into the various aspects on inflated billing of electric consumption for single phase consumers whose electromechanical meters are replaced with electronic meters. This may be very useful for all single phase consumers whose electricity bills are seems to be higher than actual consumption.

I           INTRODUCTION

Power Distribution utilities in India is facing a lot of challenges like theft of energy, improper billing, outdated technologies, poor maintenance, financial constraints etc leading to very poor financial health of the sector.

Distribution utilities have acted promptly on theft of energy & improper billing, through replacement of electromechanical meters with electronic meters. Main reasons for replacement of electromechanical meters with electronic meters are:

1.    Electromechanical meters, which were installed a few years ago, had started running slow due to moving components in the meter getting worn out.

2.    The electromechanical meters, with the passage of time and also by virtue of their design, did not record energy if load is very small.

3.    No measuring element was used in return circuit i.e. neutral wire in electromechanical meters. Tampering was easily possible in such meters e.g. reverse phase running, etc. (Detail described below with Figure-1 & Figure-2)

II          SALIENT FEATURES OF Electronic meters:      

1.    Small energy consumption by virtue of indicating lights, LEDs on switch boards, leakage of current due to old house wiring etc., gets recorded by highly sensitive and more accurate electronic meters.

2.    Some equipments e.g. TVs, DVDs, etc. when switched off through remote controls continue to consume energy unless they are switched off from the switch mounted on the equipment itself. These types of consumed energy are also recorded with electronic meters.

3.    Electronic meters are accurate and sensitive without any moving part. So sluggishness of meters were ruled out & new meters have started recording the actual energy consumption

4.    As no measuring element was used in return circuit i.e. neutral wire in electromechanical meters, tampering was easily possible in such meters e.g. reverse phase running, etc. In a tampered meter, it is possible to run the meter as and when required with simple operation of a toggle switch. To deal with tampering problems, a need was felt to have a meter, which has measuring element in neutral circuit also. So important additional design features have been incorporated in the present electronic meters i.e. measurement of current in neutral/return circuit in additional to phase circuit & measurement of higher of the two currents (one measured by measuring element in phase circuit and other by measuring element in neutral circuit.) for computation of energy consumption.

III         CAUSE OF INFLATED BILLING:

Feature of electronic meters as mentioned at point 1,2 & 3 above are providing more accurate. It is true that because of above reason there would be marginal increase in the electricity bills generated by new electronic meters as compared with old electromechanical meters. There is a feeling that the bills are inflated but it is only psychological.

But the feature of electronic meters as mentioned at point no.4 are a matter of concern and energy consumption recorded by electronic meter may be highly inflated, if neutral circuit of the household in not isolated properly.

Typical circuit of electromechanical meter is as below:

Here measuring element is used in phase circuit only. So tempering is easily possible by reversing the phase circuit as mentioned in Figure-2. If phase supply is connected to neutral of meter, neutral of meter is connected to load & other point of load is earthed,  proper voltage will applied across load & all electrical apparatus will be powered on, but consumption will be NIL, as current is not flowing through measuring coil.

So, to overcome this deficiency & to enable the utilities to trap the fraudulent consumers and to raise more accurate bills for the energy consumed by its consumers, the following important additional design features have been incorporated in the present electronic meters:

a)    Measurement of current in neutral/return circuit in additional to phase circuit.

b)    Measurement of higher of the two currents (one measured by measuring element in phase circuit and other by measuring element in neutral circuit.)

In electronic meter, if neutral circuit of any house is mixed/connected with any other house, there is possibility of highly inflated bill as described below:

Suppose you are HOUSE-2 & your all connection are perfectly alright, but your neutral is connected with neutral of HOUSE-1 and HOUSE-1 has disconnected his neutral with neutral of his meter.

As seen above, if neutral circuit of HOUSE-1 is disconnected with neutral of his meters and the same is connected with neutral of HOUSE-2, following will be the computation of energy in both houses:

FOR HOUSE-1:

Current through phase measuring coil           =          I2

Current through neutral measuring coil          =          0

Highest of the two current                              =          I2

So computation of energy (I^2*r*t) for HOUSE-2 will be OK.

FOR HOUSE-2 (Your House):

Current through phase measuring coil           =          I1

Current through neutral measuring coil          =          I1+I2

Highest of the two current                              =          I1+I2

So computation of energy for your house will be highly inflated.

There is one more possibility of inflated bill is due to leakage current from phase wire of house hold as described below.

Here actual current through household load              =          I1

Leakage Current                                                         =          I2

Current through phase measuring coil                       =          I1+I2

Current through neutral measuring coil                      =          I1

Highest of the two currents                                         =          I1+I2

So computation of energy for your house will be inflated

IV         HOW TO CHECK & REMOVE THE DEFECTs:

There is a simple check we can perform to find out whether the problem is in the new electronic meter or in the connections or household wiring etc. The current entering the meter through phase wire and coming out of the meter through neutral wire may be got checked from any qualified and experienced electrician. There could be any one of the following three observations:

1. Incoming and outgoing current is almost the same. If such is the case, then it may be concluded that connection to the meters are ok.
2. Outgoing current through neutral wire of meter is appreciably more than the incoming current through phase wire. If such is the case, then somebody else’s neutral wire has got connected to the neutral wire of your house and it is because of this reason that the meter is running fast. To be doubly sure, the following additional spot checks may be carried out:
1. Disconnect the neutral or switch off the MCB if it is installed in the neutral wire (load side). If the meter is still working, it means that there is an improper neutral connection
2. Switch off all electrical points in the house (including LEDs and indicating lamps) and check if the meter is working.  If yes, then it means that there is an improper neutral connection.  
3. Outgoing current through neutral wire of meter is less than the incoming current through phase wire. If such is the case then it means that there is some leakage of current, earthing, etc in the building. This may be because of the old worn-out wiring in the house. To be doubly sure, following additional spot check may be carried out:
1. Disconnect all your electrical gadgets in the house (including small indicating lamps) and see if the meter is working. If yes, then it means that some leakage of current is taking place in the building (see question 6 for details with regard to effect of leakage current on billing).

Call a qualified electrician, isolated your neutral circuit from other houses & change the wires which are causing leakage current.

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Decentralised Distributed Generation in Uttarakhand......Case Study

Decentralised Distributed Generation in remote villages of Uttarakhand

[Franchisee Policy by Uttarakhand Renewable Energy Development Agency(UREDA)]

SUDHIR KUMAR SRIVASTAV

AGM-RAPDRP

NTPC LIMITED, NEW DELHI

sudhirksri1@gmail.com

UREDA was established in July’2001 to develop Decentralised Distributed Generation in remote villages of Uttarakhand. Around 32 micro hydel projects along with distribution network were commissioned and 19 projects are under implementation stages. Till FY 2004-05 total cost of project were borne by UREDA and after FY 2004-05, 90% of project cost are borne by UREDA and balance 10% of project cost is borne by User’s Energy Committee.

After availability of 11 KV line of UPCL under RGGVY at the project location, UREDA has connected their 05 projects with grid and supplying power to UPCL at the cost of Rs.1.63 per unit. 90% of realized money is retained with UREDA and 10% is being distributed to Energy Committee.

For the running 32 micro hydel power projects, UERDA has facilitated to form User’s Energy Committee (Gram Panchyat / Urja Samiti) and get it registered under Panchyati Raj Act / Society Registration Act 1860 / Cooperative Society Act, trained the personal and handed over the project to Committee on 30 years lease to operate the system on no profit / no loss basis. Participation of women and SC/ST were ensured in committee. All the expenses to run the project has to be borne by Energy Committee from realization bills of sold energy. UREDA shall provide financial held for capital overhaul and major break down because of natural calamity. Return on capital investment are not the part of policy.

Formation of Energy Committee:

1. Energy committees are formed from users themselves.
2. The executive members of the committee shall represent from each beneficiary village / hamlets.
3. Executive committee members can be 7 –12.
4. Energy committee should be registered and having their own byelaws and valid bank account.
5. The Energy Committee can form 3-4 sub-committees for look after various responsibilities like:

Ø  Monitoring and supervision committee.

Ø  Material procurement committee.

Ø  Book keeping and account maintaining committee.

Role and Responsibilities of Energy Committee:

1. Regular operation of the project.
2. Repair and maintenance of different civil, electromechanical, transmission and distribution equipments.
3. Fixation of tariff for different categories of beneficiaries.
4. Regular collection of electricity bills.
5. Regular payment to operators / technicians
6. Allotment of new connections to consumers.
7. Arrangement of mandatory spares.
8. Insurance of plant and equipments.
9. Insurance of manpower.
10. Maintenance of O&M bank account.
11. Book keeping and audit of accounts.
12. Encourage for energy saving device.
13. Tariff fixation and collection of bills.

 UREDA arranges 03 month training for committee members, its operators and technicians.

To generate sufficient income for meeting all routine and annual expenditure, fixation of tariff is done in such a way that after meeting all expenditure some reserve fund is available with Energy Committee to meet unforeseen demand. For the tariff fixation, back calculation is done. Sample back calculation for 50 KW project with 150 families and 10 commercial consumers are as below is as below

Monthly Operation & maintenance expenditure:

1. 3 operator/technician @2500/-pm                            :           Rs.7500/-
2. Monthly expenditure on consumables                        :           Rs.2000/-
3. Expenditure on Insurance(@Rs18000/-pa)               :           Rs.1500/-
4. Maintenance of civil structure                                    :           Rs.3000/-
5. Miscellaneous Expenditure                                        :           Rs.1000/-
6. Reserve for annual maintenance                                 :           Rs.5000/-
                    
                                                                       TOTAL:          Rs.20000/-

Monthly Income:

1. Income from domestic consumers (36x2x150)                 :           Rs.10800/-
     (@200W per family using 6 Hrs per day i.e.
     1.2 Kwh per day or 36 Kwh per month,150 family
      at Rs.2.00 per unit)

2. Income from commercial consumers (450x3x10)             :            Rs.13500/-
    (@2000W per consumer using 8 Hrs per day i.e.
    16 unit per day or 450 unit per month, 10 consumer
      at Rs.3.00 per unit)                                                                       

                                                                             TOTAL:         Rs.24300/-

Balance available with Committee = Rs.(24300 – 20000) = Rs.4300/- pm.







Case study of some of the projects run by Energy Committee



1.   Karmi-I Micro Hydel Project:    Installed Capacity       :           50 KW
                                                            11 KV lines               :           5 Km
                                                            LT lines                      :           7 Km
                                                            Village covered          :           06
                                                            Families get benefited :           225
The above project is run by “Karmi Laghu Jal Vidyut Urja Samiti”. The samiti is registered under Society registration Act-1860. Tariff decided by the Samiti are as below:
            B.P.L. Consumers                               -           Rs.30/- pm
            Consumers using 1-5 bulbs                 -           Rs.50/-pm
            Consumers using 6-10 bulbs               -           Rs.70/-pm
            Consumers using 11-15 bulbs             -           Rs.90/-pm
            Consumers using more than 15 bulbs  -           Rs.110/-pm
            For using TV                                       -           Rs.15/-pm extra


Expenditure incurred by Samiti in one year to run the project are:
            Replacement of generator bearing      :           Rs.12000/-
            Replacement of MCCB                     :           Rs.24802/-
            Replacement of cable/conductor        :           Rs.13500/-
            Repair of equipment                          :           Rs.6500/-
            Purchase of DT                                 :           Rs.137000/-
            Payment to operators                        :           Rs.54000/-
                                                            TOTAL:         Rs.247802/-
After meeting above annual expenditure, the Samiti is having surplus money of Rs.1,85,225/-.




2.   Lathi Micro Hydel Project:        Installed Capacity       :           2x50 KW
                                                            11 KV lines               :           14.71 Km
                                                            LT lines                     :           21.68 Km
                                                            Village covered          :           14
                                                            Families get benefited :           216
The above project is run by “Lathi Laghu Jal Vidyut Urja Samiti”. The samiti is registered under Society registration Act-1860. Tariff decided by the Samiti are Rs.12/- per bulb per month for all Consumers.                             -           
           
The project is under guarantee period of manufacturer. So only payment to operator @Rs.3600/- pm is the expenditure incurred by Samiti.


After meeting above annual expenditure, the Samiti is having surplus money of Rs.70,000/-.




3.   Baicham Micro Hydel Project: Installed Capacity       :           2x50 KW
                                                            11 KV lines              :           6.4 Km
                                                            LT lines                    :           12.25 Km
                                                            Village covered         :           10
                                                            Families get benefited :           374
The above project is run by “Baicham Laghu Jal Vidyut Urja Samiti”. The samiti is registered under Society registration Act-1860. Tariff decided by the Samiti are Rs.10/- per bulb per month for all Consumers.
           
Expenditure incurred by Samiti in one year to run the project are:
            Replacement of generator carbon bush           :           Rs.5644/-
            Replacement of MCCB                                  :           Rs.13661/-
            Replacement of DT                                         :           Rs.66188/-
            DT oil & gear oil                                             :           Rs.27137/-
            Reair of turbine etc.                                        :           Rs.30461/-
            Bearing Replacement                                      :           Rs.8186/-
Civil Work                                                      :           Rs.120400/-
Repair of lines                                                 :           Rs.4890/-
Replacement of cable                                      :           Rs.16931/-
Miscellaneous expenditure                              :           Rs.23755/-
            Payment to operators                                      :           Rs.78000/-
                                                                        TOTAL:         Rs.395253/-
After meeting above annual expenditure, the Samiti is having surplus money of Rs.1,46,317/-.